Synthesis and properties of nonaromatic stable N-methylated triphyrin(2.1.1)s

Abstract

N-Methylation of 14π aromatic triphyrin(2.1.1)s by treating appropriate triphyrin(2.1.1)s with CH₃I in THF at 60 °C resulted in the formation of nonaromatic stable N-methylated triphyrin(2.1.1)s by converting one of the meso-sp² carbons to an sp³ carbon. ¹H, ¹H–¹H COSY, NOESY, and ¹H–¹³C HSQC NMR were used to deduce the molecular structures of the N-methylated triphyrin(2.1.1)s. The DFT studies revealed that the presence of a meso-sp³ carbon induced significant distortion in the nonaromatic N-methylated triphyrin(2.1.1)s, unlike planar aromatic triphyrin(2.1.1)s. The nonaromatic N-methylated triphyrin(2.1.1) 2 showed absorption features very different from those of its aromatic congeners. An intense band at 378 nm, two ill-defined shoulders at 442 and 470 nm, and a broad band in the 500–750 nm region were observed. Electrochemical studies revealed that nonaromatic triphyrin(2.1.1)s are more electron-rich than aromatic triphyrin(2.1.1)s, and computational studies are in agreement with the experimental observations.